That's why the best way to kill him is to ambush him alone. They must not wound him or fight him when his stamina is low. Which means they must not fight a prolonged battle with him.
As long as they don't give him a chance to pile up the boost from his ability, he will be easy to kill. Augustus showed how best to do it when he killed Paul while pretending to be someone who was far too weak to be a threat to the monk.
But these people don't know that. They believe that this person is truly Paul, as he looks like Paul, talks like Paul, and doesn't have an invisible weight pressing down on him.
His posture is just too straight to be Augustus. But they are not going to let him go just yet. The man explained, "We are a team formed to eliminate Augustus. We already have a way to identify him. As long as we check and see that you are not Augustus, we will let you go."
Friar Paul asked, "What method is this?"